The three roughly Earth-sized planets revolve around a star called TRAPPIST-1, which scientists describe as “ultracool.” That’s not just because they like it so much—TRAPPIST-1 is cooler and dimmer than our sun, which is why we can study its planets so easily.

The reason has to do with light—the dimmer the star, ironically, the better scientists can see the things revolving around it. In the case of TRAPPIST-1, astronomers can study the atmosphere of each of its three planets by examining how it affects light passing through it. And with enough information, scientists can determine whether those atmospheres can support life.

"Systems around these tiny stars are the only places where we can detect life on an Earth-sized exoplanet with our current technology,” said Michael Gillon, lead author of the study. “So if we want to find life elsewhere in the Universe, this is where we should start to look.”

So scientists have started to look. The next question is what they'll find.